TL;DR

• A group of trees is not a forest. Forests are complex ecosystems.
• Planting trees isn’t always good for the climate or biodiversity. It’s more important to focus on conserving old forests than planting new ones. And when planting new trees, they must be the right trees for the right location.
• Globally, forests are on the decline and about half of reforestation projects come in the form of intensively managed, largely monoculture, commercial plantations that trap 40 times less CO2 than natural forests and do not promote biodiversity.
• It is possible to “lock up” carbon in wood products like houses, furniture, and even paper to an extent. These more permanent uses of wood are much better for the climate than burning wood for fuel, which emits more CO2 than burning coal or natural gas, but eventually the rate of decay will outpace any sequestration benefits (by about 2030).

• TL;DR
• A primer on forests
• The Amazon Rainforest
• Forest fires
• Fires and climate change
• Controlled/Prescriptive burning
• Forestry
• Wood products
• Biofuel
• Monitoring & evaluation of forests
• Deforestation
• Reforestation and Afforestation
• Monoculture and tree plantations
• Forest conservation Efforts
• Resources

A primer on forests

Tree coverage ≠ forest area. A forest is not just a group of trees. It is a complex ecosystem consisting of a variety of flora, fauna, and microorganisms that all function together. Our forests sequester an estimated two billion tonnes of CO2 every year (since 2000) and so forestry offers one of the most immediate and practical solutions for climate change mitigation.

There are three general types of forests (with additional subtypes based on the amount of precipitation received). Forests cover about 31% of our global land area (as of 2020), with the majority distributed across only ten countries. More than half of all forests are found in only five: Brazil, Canada, the US, China, and Russia. Russia has the largest forested area with 20% of all global forests located there.

Tropical

• Centered around the equator
• Greatest species diversity
• Nutrient-poor & acidic soil

Temperate

• Found in the mid-latitudes
• Distinct seasons w/ a well-defined winter
• Rich soils

Boreal

• Found between 50-60°N
• Most precipitation is snow
• Thin & nutrient-poor soil

The Amazon Rainforest

The Amazon Rainforest is the world’s largest tropical rainforest, located in South America. Historically a major carbon sink, deforestation and forest fires have periodically caused the Amazon to become a source of CO2. Recent research indicates that the Amazon is likely approaching a critical tipping point where we may see significant dieback* without the resilience to recover.

*Dieback refers to an event when a group of seemingly healthy trees dies off, without an obvious cause.

Forest fires

Forest fires are most often discussed in terms of how much damage they cause. The US government alone spent $4.4 billion in 2021 on fire suppression efforts that many claim are ineffective, but the annual economic burden of fires in the US may actually be as high as $347.8 billion. One of the methods used to prevent fires, thinning, is actually having the opposite effect. The idea behind thinning is to reduce fuel for fires by selectively remote trees, but what ends up happening is we disrupt forests’ natural ability to control fires and provide more fuel in the form of quick burning underbrush.

Fires and climate change

Fire seasons are growing longer and conditions are becoming increasingly favorable for more intense and frequent fires. This creates a positive feedback loop as fires also contribute to climate change by releasing greenhouse gases into the atmosphere.

With climate change we are seeing dryer landscapes due to enhanced wildfires due to reduced rainfall and humidity and stronger winds. There is also evidence that lightning is becoming more frequent due to rising temperatures and in 2021, the Arctic region had nearly twice as many strikes as the previous nine years combined.

Controlled/Prescriptive burning

Not all fire is bad. In fact, fire can be a natural way to reduce fuel load, return nutrients to the soil, and support healthy forest growth. There are even certain species of trees and plants that need fire to grow and have evolved to release seeds when exposed to that intense heat.

The use of purposeful and controlled fires is an area where the knowledge and experience of indigenous people is especially valuable.

Forestry

Wood products

The amount of carbon stored in wood products (paper, lumber, and furniture) has been estimated to offset less than 1% of global annual emissions, but if those products are allowed to decay they become a source of carbon emissions. The amount of CO2 locked up in wooden produce will likely max out at around 441 million tonnes per year, after that it will not be able to compensate for the decay of past production (this peak in net removals is estimated to occur around 2030). Any carbon accounting benefits are locked to countries that produce products from domestic harvests.

• Mass timber: Wooden construction materials that have been engineered for strength and durability. Can replace steel and concrete in building construction for less carbon-intensive construction projects.
• Benefits: Fire-resistant (more so than steel), lightweight, faster construction time, traps CO2 (one cubic meter of CLT sequesters about one tonne of CO2)
• Concerns: Susceptible to termite damage (but can be treated to repel them); public resistance to wooden structures (mostly due to fears around fires, rot, and structural integrity); replacing the world’s steel with wood could require a tripling of today’s logging
• Examples in practice: Helsinki Wood City, Amsterdam Wooden Neighborhood, Skellefteå
• Pulp products: Wood pulp is used to make items like paper and paper products (cups, tissues, wet wipes), cardboard, LCD screens (partially), food containers, and binding agents in pharmaceuticals.
• 2020/2021 lumber price surge: There was a surge in the price of lumber during the coronavirus pandemic. Supply chain issues were compounded by wildfire, an active hurricane season, and pests. There was also an increase in demand due to a housing boom with people stuck at home doing DIY projects.

Biofuel

European and Asian countries use wood pellets as a substitute for coal and that biomass is often promoted as a carbon-neutral form of energy, but that is only true under two assumptions:

1. The biomass used is residual (branches and tops of trees that would have been left to decompose or sawdust from wood product production) and not from full trees that were cut down for energy production.
2. Net emissions are low compared to the alternative fate of the material.

Burning biomass speeds up the process of introducing CO2 into the atmosphere, versus if the material were left to decay naturally. The emissions from biomass burning can actually exceed emissions from fossil fuels, and yet the European Renewable Energy Directive of 2009 promoted biomass as a carbon-neutral energy source. Since 2009, imports of wood pellets to the EU have grown considerably.

Proponents of biomass fuel say that allowing trees to grow back will reabsorb the carbon released, but that argument is flawed. Old-growth forests absorb more carbon than new-growth forests, so there is a net gain in atmospheric CO2 from the CO2 from directly from burning the biomass + the CO2 that would have been removed by the felled tree.

Another concern around biofuel is due to land clearing for non-timber crops (or for displaced food crops) that are used to produce biofuels like corn, sugar cane, and oil palm. The average emissions of some of these biofuels are actually higher than diesel when the land-use change is accounted for.

In 2018, 800 scientists signed a letter to the European Parliament asking that biomass used for energy be restricted to only residuals and waste, and that no trees be cut for the purpose of energy production.

Monitoring & evaluation of forests

In Monitoring and Evaluation (M&E), monitoring refers to continuous assessment of a project (”what is happening?”) where evaluation is periodic and answers specific questions about a project (“did what was supposed to happen actually happen and why?”). This can be done at a large scale, to determine things like forest growth and loss, or at finer scales with specialist monitoring to look at the health and biodiversity of forests.

• Manual: Walk through the forest and perform inspections and inventories in person.
• Satellites: We have satellite images going back to 1972 in the Landsat series, and these images have allowed us to map global forest cover in a way that was not previously possible. New models allow the use of satellite data to detect areas of forest degradation and even where new forest is regrowing.
• Drones: aka Unmanned Aerial Vehicles (UAVs). Inspectors can fly drones over forests to quickly inspect large areas. Drones can be outfitted with cameras and a variety of sensors to provide additional information and have been shown to have high accuracy in performing inventories at local and regional scales. They can be a less expensive option than purchasing high-resolution satellite imagery, but require expertise in operation and image processing.

The FAO and International Model Forest Network have a variety of toolkits available to assist with executing M&E projects.

Deforestation

Between 1990 and 2020, the FAO estimates that 420 million hectares of global forest were lost to deforestation. Most deforestation today occurs in the tropics, which is leading to reduced rainfall in these regions and enhanced droughts.

Drivers of deforestation:

• Land-use change (agricultural and pastoral expansion, tree plantations, urban sprawl, mining)
• Rising temperatures and shifting biomes
• Timber production
• Woodfuel
• Natural disturbances (fire, pests, disease, severe weather)

Some local effects of deforestation (taken from 2021 IPCC report on the physical science basis):

• Decreased precipitation over the deforested area
• Increased risk of catastrophic fire due to drier conditions
• Higher likelihood of floods due to low soil infiltration and increased surface runoff
• In temperate regions: warmer summers and cooler winters

Reforestation and Afforestation

Many public campaigns have been launched around planting new trees, but forests are complex ecosystems and simply planting trees isn’t the solution to building back what we have lost. Poorly designed projects can end up doing more harm than good.

• Reforestation: Reforestation is the act of replacing trees that have been previously cut down or destroyed by natural causes like wind or a forest fire. This can be done naturally, by allowing nearby trees to spread, or artificially by physically planting seeds or sprouts. The most effective place to plant trees in terms of planet-cooling potential is in the tropics where trees grow fastest
• Concerns around reforestation:
• Planting non-native trees can lead to over-competition for resources with native species and change ecosystem function, even leading to more CO2 being released into the atmosphere.
• 45% of reforestation commitments are in the form of tree plantations for crops related to paper and rubber production. Tree plantations are detrimental to the health of our planet in multiple ways. They do not support biodiversity the way natural and diverse forests do, and when trees are harvested, carbon held within them is re-released into the atmosphere.
• Afforestation: Afforestation is very different from reforestation. It occurs when trees are planted in an area where there were previously no trees. An example would be taking an area of grassland or savanna and deliberately planting trees there. Grasslands are an important ecosystem on their own, and targeting these areas for afforestation is not always appropriate or even an effective way to sequester carbon.
• Afforestation can cause local warming or cooling effects at the surface. In areas with a lot of snow cover, like northern Europe, adding trees can decrease the amount of solar radiation reflected back into space and increase local temperatures.
• Potential consequences of afforestation:
• Increase in local warming (forests absorb more radiation than grasslands)
• Reduced water supply for local communities, especially during the dry seasons (trees will use more water than the grassland would have)
• China’s Great Green Wall: (aka Three-North Shelterbelt Program) The world’s largest man-made forest that was started as a project to stop the expansion of the Gobi Desert and shelter cities from dust and sand. The project started in 1978 and is planned to finish in 2050 having planted 100 billion trees.
• Critics of this program point to its ineffectiveness (not many of the planted trees survive and desertification continues) and that it disregards native environments and natural recovery processes—trying to control desertification through force rather than addressing the causes.

Monoculture and tree plantations

As of 2020, 45% of trees planted by countries were in intensively managed plantations. This number varies between 99% of planted trees in South America (97% being non-native species) and 6% in Europe.

Genetic diversity is a foundation of ecosystem sustainability and it’s not just plant diversity we’re talking about here, it’s all forms of life—plants, animals, fungi, and microorganisms. The overall lack of diversity in forest monoculture makes the trees more vulnerable to disease, pests, and the effects of climate change than diverse mixed forests.

Forest monoculture also causes soil compaction from heavy machinery, loss of nutrients (which then requires fertilizers), acidified soils, and changes to the regional hydrologic cycles.

Agroforestry is one example of a mixed-species plantation where woody trees are planted in combination with agricultural crops, animal husbandry, or a combination of both. Agroforestry systems must still pay careful consideration to the local environment but can reduce water consumption and reliance on fertilizers and pesticides while providing multiple income streams for farmers.

Forest conservation Efforts

This should not be considered a complete list of conservation efforts.

• Protected areas: According to the FAO, 18% of the world’s forests fall under protected areas, but these are often too small and fragmented to conserve biodiversity.
• COP26: Leaders of more than 100 countries pledged to end deforestation by 2030, but this is not the first time a promise like this has been made. Deforestation has continued since the New York Declaration on Forests of 2014 and a “Strategic Plan for Forests” by the UN in 2017.
• REDD+: (Reducing Emissions from Deforestation and Forest Degradation) A UN framework, launched at COP19 in 2013 (but in the works since 2005), designed to let industrialized countries pay developing countries to keep forests standing.
• The Forest Stewardship Council (FSC): Founded in 1993 to maintain forest management standards. A forest must meet ten principles (ranging from monitoring and evaluation to indigenous peoples' and workers' rights) in order to become FSC-certified.
• EU Forest Law Enforcement, Governance and Trade (FLEGT) Action Plan: Established in 2003 to stop the importation of illegally sourced lumber into the EU. In 2013 it became illegal to sell illegal timber on the EU market.
• EU Regulation on deforestation-free products [in progress]: Proposed Nov 2021, expected to be put into law by 2023. The goal is to guarantee that the products on the EU market do not contribute to global deforestation and forest degradation.
• Supply chain track and trace programs: Private sector initiatives to stop deforestation are often scrutinized for greenwashing and inaction but are critical as global trade is one of the major drivers of land-use change.
• It is important to recognize that growing transparency demands can increase inequalities as smallholder farmers are unlikely to be able to afford necessary upgrades, especially when there is no guarantee of a premium selling price.

Resources

• [VIDEO] Wooden skyscrapers: Sustainable homes of the future? (Cambridge University, Jun 2019)
• [FILM] More of Everything (2021)
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Experts interviewed in More Of Everything documentary
• Pronounced loss of Amazon rainforest resilience since the early 2000s (Boulton et al., 2022)
• Continuous monitoring of forest change dynamics with satellite time series (Decuyper et al, 2022)
• Doubling of annual forest carbon loss over the tropics during the early twenty-first century (Feng et al, 2022)
• Spreading like Wildfire: The Rising Threat of Extraordinary Landscape Fires (UNEP, Feb 2022)
• Commercial afforestation can deliver effective climate change mitigation under multiple decarbonisation pathways (Foster et al., 2021)
• Protecting forests or saving trees? The EU's regulatory approach to global deforestation (Henn, 2021)
• Mapping the deforestation footprint of nations reveals growing threat to tropical forests (Hoang & Kanemoto, 2021)
• Estimating Forest Structure from UAV-Mounted LiDAR Point Cloud Using Machine Learning (Neuville et al., 2021)
• Global land use changes are four times greater than previously estimated (Winkler et al., 2021)
• What the IPCC Really Says on Forest Biomass & Climate Change (NRDC, Nov 2021)
• Global Leaders Pledge to End Deforestation by 2030 (New York Times, Nov 2021)
• The U.S. Government Is Wasting Billions on Wildfire Policy That Doesn’t Work (Slate, Nov 2021)
• Climate Change Is Killing Trees And Causing Power Outages (NPR, Sep 2021)
• Logging in disguise: How forest thinning is making wildfires worse (Grist, Aug 2021)
• Parts Of The Amazon Rainforest Are Now Releasing More Carbon Than They Absorb (NPR, Jul 2021)
• ‘Fire is medicine’: How Indigenous practices could help curb wildfires (PBS, Jul 2021)
• Drivers In Each Step Of The Forestry And Logging Market Supply Chain Include Large Consumer Base, Demand For Biomass, And Automated Management (The Business Research Company, Jan 2021)
• The State of the World’s Forests 2020 (FAO)
• Planting non-native trees accelerates the release of carbon back into the atmosphere (The Conversation, Jun 2020)
• The Staggering Value of Forests—and How to Save Them (Boston Consulting Group, Jun 2020)
• The Trouble with Trees: Afforestation Plans for Africa (Bond et al., 2019)
• Restoring natural forests is the best way to remove atmospheric carbon (Nature, Apr 2019)
• How much can forests fight climate change? (Nature, Jan 2019)
• Global mitigation potential of carbon stored in harvested wood products (Johnston & radeloff, 2019)
• Climate Impacts from Afforestation and Deforestation in Europe (Strandberg & Kjellström, 2019)
• Not carbon neutral: Assessing the net emissions impact of residues burned for bioenergy (Booth, 2018)
• The role of supply-chain initiatives in reducing deforestation (Lambin et al., 2018)
• Mixed-species versus monocultures in plantation forestry: Development, benefits, ecosystem services and perspectives for the future (Liu et al., 2018)
• Europe’s renewable energy directive poised to harm global forests (Searchinger et al., 2018)
• Tropical forests are a net carbon source based on aboveground measurements of gain and loss (Baccini et al., 2017)
• Greenhouse gas emissions from tropical forest degradation: an underestimated source (Pearson et al., 2017)
• Taking Down the “Great Green Wall”: The Science and Policy Discourse of Desertification and Its Control in China (Jiang, 2016)
• Seeing the forest from drones: Testing the potential of lightweight drones as a tool for long-term forest monitoring (Zhang et al., 2016)
• Would you live in a wooden skyscraper? (Science, Sep 2016)
• High-Resolution Global Maps of 21st-Century Forest Cover Change (Hansen et al., 2013)

Last updated: Nov 2022